INVESTIGATION OF NON-DESTRUCTIVE TESTING OF ULTRASONIC OF FOUR-SHEET STACK OF JOINTS AND FORMULATION OF ITS APPLICATION IN THE AUTOMOTIVE INDUSTRY.

The spot welding process is one of the most common and oldest methods of electric welding, which is widely used today in various industries, especially automotive, aerospace, electronics and some parts of the nuclear industry. It has a point in the construction of an automobile body of between 2000 and 5000 bits. Spot welding quality control is carried out according to international standards, which is often accompanied by demolition of samples. The use of a destructive method in controlling the quality of spot welding created on different parts or the entire body of the car costs a lot. Which will be saved in case of quality control of these points using non-destructive method and sales of welded parts. Accordingly, a non-destructive method should be used to evaluate and control spot welds. One of these methods is a non-destructive ultrasonic test that has been successfully used in this project. The ultrasonic waves measure the diameter of the boiling button, which is an important indicator of boiling quality. In this study, a large number of healthy and defective point welds were made and these specimens were tested by ultrasonic non-destructive methods and destructive testing of pull-shear testing. The results of these experiments showed that the ultrasound test can detect defective welds well and its results in the production line also improve the test method. Keywords: Spot resistance welding, Welding nugget, Ultrasonic Test, Automotive Industry